This invention relates generally to an optical inspection method for determining the proper engagement of a threaded fastener into the mated opening of a workpiece and more specifically to an automated method employing particular light source means to evaluate certain physical parameters associated with the already engaged fastener.
Various inspection method are already widely used to automatedly evaluate the physical dimensions and/or profile of threaded fasteners. One method uses contact probes which touch the fastener at various points to determine if its dimensions or profile meet the inspection criteria. Use of such contact means has inherent limitations, however, by reason of contact wear and a requirement for accurate positioning during the particular evaluation process. Moreover, such inspection systems are generally slow to operate and can be limited in performance by the complexity of the particular fastener being evaluated. A variety of non-contact inspection systems are also now being used for this purpose, including automated optical systems as a means for characterizing the physical parameters of a threaded fastener, such as machine bolts and threaded plugs. For example, laser gauging systems are used in which the specific dimensional measurements of a threaded fastener can be evaluated. A representative laser inspection system enabling machine bolts to be sorted by automated means before being affixed to the workpiece is disclosed in U.S. Pat. No. 5,568,263.
There understandably remains a need for inspection of the threaded fastener after being affixed to the workpiece. Assembly line manufacture of automotive vehicles and many other products requires speedy detection of any improperly engaged fasteners during the assembly process. misalignment or cross threading of the fastener after being affixed to the workpiece can serious disrupt or disable the manufacturing process. Likewise, a failure to have the assembled fastener entirely threaded into the workpiece can cause similar harm. It would be further desirable that such novel inspection method be easily adapted for convenient use with existing assembly equipment during manufacture of a final product.
It is an object of the present invention therefore to provide a novel inspection method enabling detection of improperly engaged threaded fasteners after having been affixed to the workpiece.
It is another object of the present invention to provide an optical inspection method employing a particular array of laser devices to evaluate the height of an affixed threaded fastener above the workpiece.
It is also an object of the present invention to provide an optical inspection method employing a particular array of laser devices to evaluate any misalignment of the affixed threaded fastener.
It is a still further object of the present invention to provide an optical inspection method enabling detection of improperly affixed threaded fasteners by automated means.
These and still further objects of the present method are achieved by (a) orienting a plurality of laser devices around the circumference of an already engaged threaded fastener at a remote location therefrom, (b) projecting the beams from all said lasers to intercept the head end of said engaged threaded fastener at a predetermined angle with respect to the top surface of said threaded fastener head end, (c) detecting a gap distance in said projected laser beams after interception with said head end of said already engaged threaded fastener employing remote video means, and (d) utilizing the length of said gap distance with data processing means to automatedly determine proper engagement of said threaded fastener. In a preferred embodiment, three or more laser devices are disposed approximately equidistant around the circumference of said already engaged threaded fastener, the projected beams from all said lasers intercepting the center region of the head end of the engaged threaded fastener at an acute angle with respect to the top surface of said threaded fastener head end, detecting the gap distance in said projected laser beams after interception with said head end of said already engaged threaded fastener employing a remote video camera, comparing the gap distance for the individual projected laser beams, and utilizing any differences found in said gap distances to automatedly determine proper engagement of said threaded fastener. In said manner, the height of the already engaged threaded fastener above the surface of the workpiece to which it has joined can be determined for conformity with acceptance values previously stored in the selected data processing means. The gap distances measured in said manner are also found to be proportional to the height of the already engaged threaded fastener above the surface of the workpiece to which it has been joined. In a similar manner, such automated comparison of gap distances for the projected laser beams can determine any cross threading of the already engaged fastener. Thus, finding no significant difference in gap distances between individual projected laser beams determines that the head end of the already engaged threaded fastener lies reasonably parallel to the surface of the workpiece to which it has been joined. It can be appreciated that increasing the number of laser beams being employed in the present inspection method favorably provides more data values to be lodged in the associated data processing means. Additionally, the employment of computerized analysis equipment such as common machine vision inspection type apparatus, and the like, is contemplated for automated processing of the gap length comparisons being made in the present inspection method. It is contemplated that the present inspection method can be as effectively conducted with threaded fasteners engaged in a vertical direction as well as when engaged at angles other than vertical.